The Lifegard Aquatics 15W GT5 UV Sterilizer Lamp for 15W QL-Series UV sterilizers and the Aquastep Pro 15 Watt UV Sterilizer. This is also the correct replacement lamp for the discontinued 8W and 10W QL-Series UV Sterilizers (although the lamp will only put out 8W and 10W respectively). This lamp will not work with the old style Aquastep 15 Watt UV Sterilizer.